1. Field of the Invention
The present invention relates to a composite article comprising a copper element, e.g. a copper printed circuit and an adhesive material, and a process for producing such an article. The invention is particularly, but not exclusively, applicable to a multi-layered wiring circuit board and also is applicable to other articles in which copper is bonded to an adhesive material such as semiconductor chip packages, flexible printed circuits and a tape automated bonding device.
2. Description of Prior Art
In FIG. 1 described in detail below there is shown a conventional multi-layer wiring circuit board. In the manufacture of such a board, individual circuit boards carrying copper wiring layers are laminated in a stack alternately with layers of adhesive material known as prepregs which are cloth layers impregnated with thermosetting polymers. To achieve bonding, the stack is subjected to pressure and heat. The present specification is especially concerned with the bonding between the copper layer and the adhesive material.
U.S. Pat. No. 4,642,161 (JP-A-86-176192) describes a process in which a conventional multi-layer printed wiring board is produced by roughening the surface of a copper circuit layer by an etching treatment, carrying out a "blackening treatment" to form a copper oxide film by oxidation, effecting reduction of the copper oxide and thereafter carrying out lamination and bonding with prepreg layers. In this case, the surface of the copper foil has pit-like recesses having a diameter and depth of from 0.1 to 1.0 .mu.m, due to etching.
U.S. Pat. No. 4,643,793 (JP-A-86-15981) discloses a method of treating a surface for copper to improve its adhesion to prepreg material. The surface is electrolessly plated by contacting it with an aqueous solution containing (a) copper ions, a chelating agent, a reducing agent, hydroxy ions and water, and (b) a nitrogen-containing heterocyclic compound which colors the surface into a color and gloss other than that of metallic copper. Thereafter the surface is treated with at least one of ammonia water, an aqueous solution of a reducing agent and an acidic solution. It is stated that the treatment by the first solution can form a copper deposition layer having minute particles, needles or cylinders or mixtures thereof. Etching to roughen the surface prior to the electroless printing is described.
U.S. Pat. No. 3,615,737 discloses an electroless metal deposition solution containing a small amount of extraneous ions such as ions of vanadium, antimony, arsenic and bismuth. It is stated that the solution provides enhanced ductility of electroless metal deposits.
U.S. Pat. No. 4,632,852 (JP-A-86-9578 and JP-A-86-38406) discloses a process for electroless copper plating suitable for thick plating in the production of printed circuit boards. Inorganic germanium compounds or silicon compounds are added to the plating solution, and plating is carried out while injecting an oxygen-containing gas into the solution and/or with an oxidizing agent in the solution. It is said that an improvement of the mechanical properties of the plating film are achieved.
JP-A-77-79271 discloses a process for manufacturing a multi-layer printed circuit board, which comprises roughening the surface of desired circuit patterns by plating a patterned copper film by electroless metal deposition and laminating a plurality of the treated printed circuit boards. The adhesion strength between the treated circuit boards can be improved.
The conventional techniques for producing multi-layer wiring circuit boards can obtain sufficiently high bonding strength between a copper circuit and a prepreg resin in the case where known resins such as an epoxy resin, a polyimide resin, and the like are used and can secure high reliability of the printed wiring board.
However, there is a need to improve bonding of the copper to the adhesive. Novel resins exist whose properties such as heat resistance, thermal expansion coefficient and the like are improved permitting high density wiring and high computation speed of the printed circuit but these have low affinity with respect to copper and known techniques cannot obtain sufficiently high bonding strength. Accordingly, sufficient reliability cannot be obtained in the multi-layer printed wiring board.
Secondly, the conventional techniques make the copper surface coarse by etching, but if the etching conditions are not appropriate the circuit is excesively etched locally and the connection reliability of the wiring tends to be reduced.